[Django] #19625: mysql 5.1 large decimalfield lookups return too few results

[Django]

#19625: mysql 5.1 large decimalfield lookups return too few results
----------------------------------------------+--------------------
     Reporter:  wdoekes                       |      Owner:  nobody
         Type:  Uncategorized                 |     Status:  new
    Component:  Database layer (models, ORM)  |    Version:  master
     Severity:  Normal                        |   Keywords:
 Triage Stage:  Unreviewed                    |  Has patch:  0
Easy pickings:  0                             |      UI/UX:  0
----------------------------------------------+--------------------
 It seems that there is a bug in the mysql 5.1 (and probably lower)
 conversion of strings to decimals. Since Decimal value lookups are always
 passed to the mysql backend as strings, Django is affected.

 See this example:
 {{{
 mysql> select version() as server_version\G
 *************************** 1. row ***************************
 server_version: 5.1.66-0+squeeze1-log
 ...
 mysql> create table abc (value decimal(31,0));
 ...
 mysql> insert into abc values (1234567890123456789012345678901);
 Query OK, 1 row affected (0.00 sec)

 mysql> select value from abc where value =
 1234567890123456789012345678901\G
 *************************** 1. row ***************************
 value: 1234567890123456789012345678901
 ...

 mysql> select value from abc where value =
 '1234567890123456789012345678901'\G
 Empty set (0.01 sec)
 }}}

 Obviously, a fix could be to upgrade to a newer MySQL server version --
 the MySQL 5.5.28 I tested didn't have this issue -- but that isn't always
 possible.

 I suppose a workaround/fix might not be included in Django because the bug
 lies in MySQL, but I'll file it here for the record.

 Test cases are included:
 {{{
 FAIL: test_decimal_field_broken1 (test_long_decimal.tests.DecimalTests)
 ...
 AssertionError: book with isbn 1234567890123456789012345678901 was not
 found
 }}}

 I tried to work around the bug by surrounding a decimal value in lookup
 with CAST(..), but that (sometimes!) triggers an SQL Warning (in other
 tests!) instead:
 {{{
 ERROR: test_decimal_field_works1 (test_long_decimal.tests.DecimalTests)
 ...
 Warning: Truncated incorrect DECIMAL value: ''
 }}}

 So, my easy fix did not work out as expected.

 The proper fix, if any, would probably to force the backend to take the
 decimal as an *unquoted* value. But I didn't find an easy path to achieve
 that.

 Regards,
 Walter Doekes
 OSSO B.V.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/19625>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

-- 
You received this message because you are subscribed to the Google Groups 
"Django updates" group.
To post to this group, send email to django-updates@googlegroups.com.
To unsubscribe from this group, send email to 
django-updates+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.